The present invention relates to the filtering of a gas stream for the removal of particulate matter entrained therein via a fabric filter, and more particularly, to a method for detecting the existence of an overload of the fabric filter due to the accumulation of particulate matter collecting on the fabric filter.
One highly successful technique for separating undesirable particulate matter from a gas stream laden with particulate matter is fabric filtration. Such filtration is typically carried out in a fabric filter apparatus, commonly referred to as a baghouse, which houses fabric filter means upon which at least a portion of the particulate matter in the gas stream traverses the filter means. Typically, the baghouse is comprised of one or more filter chambers housing a plurality of fabric filter bags suspended from a skeletal support system. The particulate matter-laden gas stream enters the baghouse from one end and, under the influence of a fan either disposed upstream or downstream of the baghouse, passes through the filter bags and out the opposite end of the baghouse, with the particulate matter being retained on the upstream side of the filter bags which the gas must traverse as it flows through the baghouse. The gas that is discharged from the baghouse is a relatively particulate matter-free gas stream and vented to the atmosphere.
Continuous operation of such a filter apparatus causes a cake of particulate matter to build up on the upstream surface of the filter bags or other fabric filter means. As this cake of dust builds up on the surface of the filter means, the pressure drop across the filter means increases whereupon it ultimately becomes necessary to effect removable of the filter cake so as not to exceed the pressure-volume capabilities of the flow of inducing fan. Therefore, it has become customary to effect removal of the particulate matter cake building up on the filter means on a periodic basis when the pressure differential or drop across the baghouse has reached a preselected upper limit of desired operating-pressure differential.
In a single chamber collector, it is customary to clean only a portion of the plurality of filter bags housed therein during any given cleaning operation while the remaining filter bags continue to filter the particulate laden gas stream. Typically, when the gas pressure drop between the inlet flange and the outlet flange of the collector has reached the upper limit, the cleaning of a first portion of the filter bags is initiated and continue for a preselected period of time. The clean filter bags are then returned to service and the cleaning of a further portion of the filter bags is initiated. This cleaning sequence is continued either until all filter bags have been cleaned or the pressure drop across the dust collector has reached a preselected lower limit value even though all of the individual filter bags may not have been cleaned in this particular cleaning sequence.
In a typical multiple chamber collector, each individual chamber may be isolated from gas flow independently of the remaining chambers which remain in service. Typically, when the gas pressure drop between the inlet flange and the outlet flange of the collector has reached this upper limit, the cleaning is initiated by isolating one of the chambers of the collector and cleaning that chamber, then sequentially isolating and cleaning each of the remaining chambers until all chambers of the dust collector have been cleaned in fairly rapid succession. Alternately, the cleaning process may be terminated at a predesignated lower limit value on pressure drop across the dust collector even though all of the individual chambers may not have been cleaned in that particular cleaning sequence.
In either case, there is a significant decrease in pressure drop across the dust collector from the initiation of the cleaning sequence to termination of the cleaning sequence. Normally, there is also a decrease in pressure drop across the dust collector as a result of each of the individual cleaning steps in the cleaning sequence. However, it is possible for the pressure drop across the dust collector to have significantly decreased over the cleaning sequence, even though the pressure drop may have even increased during one or more of the cleaning steps forming the cleaning sequence due to a malfunction in the cleaning process.
That is, even though the pressure drop across the dust collector may have decreased to a lower pressure drop after completion of the entire cleaning sequence, it is possible that a certain portion of the filter bags or one particular chamber may not have been effectively cleaned during a cleaning step in the cleaning sequence.
In the typical prior art system, the operator would have no way of knowing that a portion of the filter bags or one particular chamber was experiencing an overload due to ineffective cleaning. The operator would continue operation of the collector unaware of the overload because the pressure drop across the dust collector would have decreased over the entire cleaning squence despite one or two ineffective steps in the sequence. Continued operation in an overload condition would most likely result in damage to the overloaded filter bags.